This invention pertains to the electrical interconnections of the salient poles of a dynamoelectric machine's rotor and, more particularly, to a system for connecting the salient poles of a hydrogenerator whereby the poles, while being connected in series, each assume an opposite magnetic polarity than their adjacent neighboring poles.
Hydrogenerators typically have rotors constructed of a rotatable shaft with a cylindrical rim on which an even number of salient poles are mounted. The shaft may be aligned vertically with a connection to a turbine at the lower end. The salient poles are mounted about the periphery of the cylindrical rim with each salient pole being of opposite electromagnetic polarity than its immediately adjacent neighboring poles.
Each salient pole contains a helically wound field coil and the alternating polarity can be accomplished in two basic ways. First, the salient poles can have their field coils wound in such a way as to have half of them wound in a direction to produce a magnetically north field and the other half of them wound to produce a magnetically south field when a field current is passed through the field coil in basically the same manner. Second, as in the present invention, the salient poles all have their field coils wound identically but are connected in series in such a way as to provide opposite current flow directions in the north poles than in the south poles.
Both of these methods can present disadvantages, either in manufacturing the poles themselves or in electrically connecting the poles during their final assembly on the cylindrical pole-carrying rim. The first method requires two different designs, depending upon the polarity of the pole, which can not only complicate the manufacturing process but increase the number of spare poles required after installation to insure preparedness in the case of a breakdown involving the salient poles. Also, during field repair operations, care must be taken in replacing the poles to insure that the faulty pole is replaced by an identically wound one.
In the alternative, if all salient poles are identically wound, the polarity alternation between poles must be accomplished by a connection system external to the salient pole itself. This connection system must not be so complex as to lessen the advantages gained by using identically wound salient poles. Considerable savings can be achieved if all salient poles can be wound identically and each can be electrically connected during final assembly in a similar manner, regardless of polarity.
The present invention relates to an electrical connection system for connecting identically wound salient poles in series while producing opposite electromagnetic polarity in alternate poles. A hydrogenerator with a rotor of salient pole construction as referred to in this application is described in detail in U.S. Pat. No. 4,303,842 which issued to R. D. Nathenson, on Dec. 1, 1981 assigned to Westinghouse Electric Corporation and incorporated by reference herein. The present invention specifically relates to the salient poles of a hydrogenerator rotor which has a generally cylindrical pole mounting rim at the upper end of a vertically mounted rotatable shaft and, more specifically, to a rim having indentations in its upper planar surface in which the connections are made.
The indentations serve the primary purpose of providing the space required to make the required electrical connections and, in water-cooled hydrogenerator rotors, piping connections. An indentation is located proximate the point where each salient pole is mounted to the rim and provides an opening through both the peripheral and planar surfaces of the rim. The position of the indentation allows access to the location of the present invention radially inward from the salient pole in a horizontal direction and vertically downward from the cylindrical rim's upper planar surface. Locating the present invention in these indentations shortens the required length of connecting straps while making access possible from above during assembly operations and reducing the total volume required for the connection system of the present invention. Since the present invention is thus positioned below the upper planar surface of the cylindrical rim, less space is required for the connection apparatus.
The present invention comprises, for each pole, two rigid conductive leads, two flexible conductive straps, a threaded stud, an insulative cylindrical sleeve, two conductive tabs, and an insulative separator. Each lead is generally Z-shaped and most probably made from flat bar stock. One end segment of each lead has a round hole therethrough, large enough to accommodate the threaded stud with the insulative cylindrical sleeve disposed around the stud.
The two leads are positioned within the rim's indentation and with their holes aligned coaxially. Furthermore, the two leads are aligned such that they extend in opposite directions from the axis of the holes and combine to form a line which is generally perpendicular to the radius of the cylindrical rim. The dimensions of the leads are such that their segments with holes lie near the bottom surface of the indentation, their central segments are generally perpendicular to the upper planar surface of the cylindrical rim and their remaining segments lie adjacent to and generally parallel with the upper planar surface of the cylindrical rim.
The threaded stud is disposed within the insulative cylinder which is itself disposed through the two coaxial holes. In order to mechanically fasten the two leads to the bottom surface of the indentation, the threaded stud is disposed into a threaded hole in the bottom of the indentation with the other end of the stud being disposed into a threaded nut. The two leads are thus fastened together and to the cylindrical rim with the insulative separator disposed between them to prevent electrical contact between the two leads.
One of the conductive tabs is connected to the segment of each lead which has the hole therethrough and is connected generally perpendicularly to the upper planar surface of the cylindrical rim. These tabs provide a point of electrical connection between the lead to which it is connected and the field coil of the salient pole. The positioning of the tabs on the leads determines the eventual polarity of the salient pole. By positioning the tab between the hole and the vertical segment of its lead, one polarity is achieved. Alternatively, by positioning the tab between the hole and the vertical section of the other lead, an opposite polarity is achieved. The polarities are determined by the positioning of the tabs since the present invention also connects each tab to the closest of two connection points of the salient pole which are generally radially outward from the two tabs. The connection between each tab and its closest pole connection point is made by flexible conductive straps and, due to the nature of the present invention, no crossover connections are required for either north or south polarity connections.